TOPIC:

+1 on the mileage concerns, yes it could be thrashed but that is more likely from neglect than mileage, the GPz 750 parts bike I had had about 40k on it and had been dismantled purely because the owner decided to sell it as spare parts rather than a complete bike. The parts I've looked at including the head that I sold, all look great with no obvious signs of wear. Most likely head problem would be the oil seals, you'd be regrinding valves etc. anyway if doing a rebuild, it would be a good time to replace the valve springs or upgrade them.

I don't know much about 810 kits, but presumably they are either different for various 750 models, or the pistons are designed so nothing tangles regardless of the head and model. If you got a GPz head and then an 810 kit that will work for a GPz750 it seems that would resolve most of your issues, unless of course your bores turn out to be perfect

My 750E engine bores were showing wear even though the bike had only covered 10k miles. I think Kawasaki didn't spend much effort controlling piston to cylinder fit either because even when measured at places where the piston doesn't run, the bores were above nominal. At the end of the day I just threw new rings in and the engine runs good. If I could have found Kawasaki OS pistons and rings I would have bought them. I didn't want to punch it out to 810.

Daftrusty wrote: These are all good points!
I failed to elaborate on my current engine and the plans I have for it, so I should fill in the blanks...

My current engine is a bone stock 1981 kz750e motor with 25,000 miles- 74bhp
Compression test shows 150psi on all cylinders and leakdown shows 10%
Leaking Upper oil seals at the head gasket are forcing me to dig into the topend.

Other 750 variations and options to choose from:
1982 gpz750r1 - 80hp from factory ported and polished heads with squish band, different cam profile, 9.5:1 pistons and freer flowing carbs.
83-86 gpz750 (zx750a) is 84bhp due to better designed head with squish band, .5mm countersunk exhaust valve to promote better intake flow (hence the smaller base circle on the exhaust cam)and no longer ported from factory, redesigned hotter cams, 9.5:1 pistons and freer flowing CV carbs.
Zephyr zr750 and zr-7s - 76bhp using same cams as the 1982 gpz750, Squish band head (without the fancy exhaust valve chamber or porting) 9.5:1 pistons, cvk32 carbs

Hopes for my engine;
I'm aiming for the some of the added power of the gpz750 but with the torque being lower down in the power range to make it more usable....
My cylinder head is very good condition other than needing a valve job I suspect,
so I"m trying to do any number of things to increase power without having to buy a used GPZ head.

What I have planned:
Fully rebuild head
cvk32 carbs from zr750 (already purchased and rebuilt...just waiting on how to jet them)
4-1 exhaust (already purchased Kerker)
Oil cooler ( already setup with zr-7 oil pan and zr550 oil cooler)
Higher volume zr-7 oil pump (still not sure if this is necessary)
zr-7 starter clutch
Updated CDI Ignition ( already have complete CDI ignition system from zr750 including pickups and coils already integrated into wiring harness)
zx750 Intake cam ( still not sure if mixing gpz intake cam with the stock exhaust cam will move the torque lower down in the power band like I want)
810 kit and/or zx750 pistons ......which brings us here

And will eventually go into this:

Hopefully that clears up my intentions....or complicates everything...I don't know anymore

82 KZ750R1 has standard 750 cams and 34mm Mikunis.

p.s. I would just freshen the head.

Nessism wrote: My 750E engine bores were showing wear even though the bike had only covered 10k miles. I think Kawasaki didn't spend much effort controlling piston to cylinder fit either because even when measured at places where the piston doesn't run, the bores were above nominal. At the end of the day I just threw new rings in and the engine runs good. If I could have found Kawasaki OS pistons and rings I would have bought them. I didn't want to punch it out to 810.

I think Kawasaki's attention to quality went down considerably after 1980 on the KZ's and their close brothers like the GPz's. When they started building the Z1's they really went to town to build the best motorcycle they could, that's why those bikes had such fantastic and expensive paint jobs on their tanks, gradually as they became popular and Kawasaki successful, they started cutting some corners IMO. The J bikes had a lot of bore issues from the factory and were known for various issues as a result including oil consumption. There were a lot of other things as well that didn't seem as robust and well finished as the earlier bikes, I say this from my experience with an almost new Z1000J I had in the UK in 1982. Still great bikes though, look how many are still out there today pretty much original and running.

82 KZ750R1 has standard 750 cams and 34mm Mikunis.

You are 100% correct. The only difference was the the exhaust cam no longer came with a tach drive gear. My mistake came from reading a 1980's tech article on the gpz750r1 that said it had the same came timing as the kz750e, but different lobe profile to speed up valve opening. That must be bunk!

I'm glad to hear that 40k is not that bad for a head. My only worry is that this bike at the salvage yard has been lying on its side for years with no carbs on it and the exhaust pulled off but the plugs are still in. So its going to be crusty inside.

The green KZ650 in my avatar has GPZ750 pistons even with a KZ650 head, so GPZ750 pistons in a KZ750 should be simple.

I was sure I had heard of people putting gpz pistons in the kz650's, but I was unsure if they had to do any fancy head work to make it work, other than machining the case to make room for the 750 cylinder block. I need to research that more!

I also need to find a day to go out to the garage and remove the top end and have the bores checked for clearances and the state of the valve seats and guides. That will dictate to me my options of 810 or gpz pistons and maybe a '82 gpz head.

Thanks again for all the input!